Possible Male Birth Control Blocks Sperm

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Keeping sperm from being ejaculated may provide the key to
creating a birth control drug for men, according to a new mouse
study.

The research is far from translating to a pill that human males
could pop to keep from making babies; to reach that stage, any
drug would have to undergo years of testing for safety and
effectiveness. Nevertheless, the study offers hope for a new
method of birth
control for men, the researchers said.

"The search for a viable
male contraceptive target has been a medical challenge for
many years," Sabatino Ventura of Monash University in Australia
and colleagues wrote today (Dec. 2) in the journal Proceedings of
the National Academy of Sciences.

The challenges of male birth control

Compared with female birth control, the male version is a
biological challenge. Instead of stopping one egg, male birth
control would have to stop each of the 1,500 sperm cells men
produce each second. Early tests have proven hormonal methods to
be clumsy, causing too many side effects. Attempts at halting the
rapid production of sperm is similarly difficult, in part because
a natural barrier between the blood and the testis, the site of
sperm production, keeps drugs out.

To be popular, any anti-sperm birth control method would also
need to be reversible, and could not cause long-term damage to
sperm cells, lest it lead to birth defects when a man did decide
to have children. [ Sexy
Swimmers: 7 Facts About Sperm ]

The new study attempts another path: Instead of blocking the
production of sperm, researchers are now trying to block its
transport.

Sperm are made in the
testes, and stored in a tightly coiled tube called the
epididymis, inside the testicles. When a man ejaculates, smooth
muscle propels the sperm out of the epididymis, through a tube
called the vas deferens, into the urethra and out of the body.
Receptors on the muscles receive hormonal signals that instruct
the muscles to contract, sending the sperm on its way.

Previous attempts to block these receptors, known as
α1A-adrenoceptors and P2X1-purinoceptors, had decreased male
fertility, but not entirely — male mice with blocked
receptors could still father offspring up to 50 percent of the
time.

But such studies had attempted to block only one of the two types
of receptors. Most likely, Ventura and his colleagues reasoned,
the body could compensate by beefing up the unblocked kind.

In the new study, the researchers bred mice that lacked both
α1A-adrenoceptors and P2X1-purinoceptors. They found that female
mice without the receptors could still reproduce as normal. Male
mice pursued females and mated with them as usual, but they never
sired babies.

A male pill?

A closer look revealed that the male mice without the receptors
produced normal sperm, and when that sperm was used in artificial
insemination attempts, it resulted in normal baby mice. The
mice's vas deferens, however, did not contract normally in
response to stimulation, suggesting that the lack of receptors
did stop sperm movement.

The two blocked receptors are also important for cardiovascular
health, but the mice showed few side effects beyond a 10-percent
decrease in blood pressure, the researchers found. More work on
side effects will need to be done, but the study suggests that
men taking drugs to block the receptors would not be in danger,
the researchers wrote.

The vas deferens is located outside of the blood-testis barrier,
meaning that oral contraceptives targeting the receptors could
easily reach their target. In fact, drugs that block
α1A-adrenoceptors are already on the market to treat benign
prostate enlargement.

A drug that blocks the P2X1-purinoceptor would still need to be
developed and tested.

Of course, even if a combination α1A-adrenoceptor and
P2X1-purinoceptor–blocking drug were developed, men would have to
be on board, psychologically. The anti- α1A-adrenoceptor drugs
already on the market have the side effect of the occasional
orgasm
without ejaculation.

"A lack of ejaculate has the potential to be disconcerting," the
researchers wrote in their study.